This invention relates to a rotary drilling chuck suitable for use in diamond drilling.
A rotary drilling chuck which can be released hydraulically and which will fail safe in the absence of hydraulic power has already been proposed in the specification of U.S. Pat. No. 3,692,320. In the latter specification clamping jaws are acted upon by an axially moving chuck hood which in turn is acted upon by belleville springs around pairs of long screws which also extend axially. The result is that the extent to which a rod can drill between successive chucking operations is decreased by the distance which the hood and its associated hydraulic mechanism takes up over the distance which is actually required for clamping.
It is an object of the invention to provide drill chuck which can be released hydraulically and which will fail safe in the absence of hydraulic power, but which occupies a relatively short distance in the drilling direction so that the stroke between chucking events is as large as practicable.